Cutting insert, cutting tool, and method of manufacturing machined product using the same

ABSTRACT

A cutting insert of an embodiment of the present invention includes an upper surface, a lower surface, a side surface connected to each of the upper surface and the lower surface, and an upper cutting edge located at an intersection of the upper surface and the side surface. The lower surface includes a mount part having alternately three first top portions spaced a distance a away from a central axis extending between the upper and lower surfaces and three second top portions spaced a distance b away from the central axis in a bottom view. The mount part further has a concave part including at least the central axis. The second top portions are located closer to the upper surface than the first top portions. A cutting tool with the cutting insert, and a method of manufacturing a machined product by using the cutting tool are also provided.

FIELD OF INVENTION

The present invention relates to a cutting insert, a cutting tool, and amethod of manufacturing a machined product using the same.

BACKGROUND

Conventionally, as a cutting insert (hereinafter referred to as an“insert” in some cases) used for performing a face milling process, aninsert whose both hexagonal shaped surfaces are usable has been proposed(for example, refer to International Publication No. 2007/037733).

According to the insert of the International Publication No.2007/037733, a flat surface is formed on an upper surface as shown inFIGS. 1A and 1E thereof. The flat surface functions as a mount surfacebrought into contact with an insert pocket when a cutting edge locatedcloser to a lower surface is used.

The above insert is generally obtained by subjecting raw material powderto press molding and firing. However, deformation may occur during thefiring due to shape factor and firing environmental variations or thelike. For example, even when the surface functioning as the mountsurface is molded flat, the deformation may occur by the firing.Consequently, the mount surface of the insert is brought into contactwith a position different from an intentional position at a designstage, and thus there is a risk of deterioration of attachmentstability.

SUMMARY

An object of the present invention is to provide a cutting insert and acutting tool each having excellent attachment stability, as well as amethod of manufacturing a machined product using the cutting insert andthe cutting tool.

A cutting insert according to an embodiment of the present inventionincludes an upper surface, a lower surface, a side surface connected toeach of the upper surface and the lower surface, and an upper cuttingedge located at an intersection of the upper surface and the sidesurface. The lower surface includes a mount part having alternatelythree first top portions spaced a distance a away from a central axisextending between the upper and lower surfaces and three second topportions spaced a distance b away from the central axis in a bottomview. The mount part further has a concave part including at least thecentral axis. The second top portions are located closer to the uppersurface than the first top portions.

A cutting tool according to an embodiment of the present inventionincludes the cutting insert of the foregoing embodiment, and a holderconfigured to attach the cutting insert thereto.

A method of manufacturing a machined product according to an embodimentof the present invention includes: rotating the cutting tool accordingto the foregoing embodiment on a basis of a rotation axis of the holder;bringing the upper cutting edge of the cutting tool being rotated intocontact with a surface of a workpiece; and separating the cutting toolfrom the workpiece.

In the cutting insert according to the embodiment of the presentinvention, the lower surface includes the mount part having alternatelythe three first top portions spaced the distance a away from the centralaxis extending between the upper and lower surfaces and the three secondtop portions spaced the distance b away from the central axis in thebottom view. The mount part further has a concave part including atleast the central axis. The second top portions are located closer tothe upper surface than the first top portions. Thus, the mount part hasthe concave part and hence the mount part is difficult to contact withthe contact surface of the holder in the vicinity of the central axis.It is therefore ensured that the first top portions and the second topportions, each being located closer to the outer edge, function as afixing point brought into contact with the contact surface of theholder, thereby improving attachment stability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a cutting insert according to anembodiment of the present invention;

FIG. 2( a) is a plan view (top view) of the cutting insert shown in FIG.1;

FIG. 2( b) is a bottom view thereof;

FIG. 3( a) is a view of the cutting insert shown in FIG. 2( a),specifically a fragmentary side view taken in the direction indicated byarrow A;

FIG. 3( b) is a sectional view thereof taken along line B-B;

FIG. 4( a) is a view of the cutting insert shown in FIG. 2( a),specifically a partially enlarged view of a cross section taken alongthe line B-B;

FIG. 4( b) is a partially enlarged view of a cross section taken alongline C-C therein;

FIG. 5( a) is a perspective view of a cutting tool according to anembodiment of the present invention;

FIG. 5( b) is a side view thereof;

FIG. 6( a) is a side view showing in enlarged scale an attachmentcondition of the cutting insert in the cutting tool of FIG. 5,specifically a view of the cutting insert taken from a side surfacethereof;

FIG. 6( b) is a view of the cutting insert taken from an upper surfacethereof;

FIG. 7( a) is a perspective view of a holder in the cutting tool shownin FIG. 5;

FIG. 7( b) is a partially enlarged perspective view of an insert pocket;

FIG. 7( c) is a partially enlarged side view of the insert pocket;

FIG. 8( a) is a sectional view of the cutting tool shown in FIG. 6( b),specifically a partially enlarged view of a cross section taken alongline E-E therein;

FIG. 8( b) is a partially enlarged view of a cross section taken alongline F-F therein;

FIG. 8( c) is a partially enlarged view of a cross section taken alongline G-G therein;

FIGS. 9( a) to 9(c) are process drawings showing a method ofmanufacturing a machined product according to a first embodiment of thepresent invention; and

FIGS. 10( a) to 10(c) are process drawings showing a method ofmanufacturing a machined product according to a second embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Cutting Insert

A cutting insert according to an embodiment of the present invention isdescribed in details below with reference to FIGS. 1 to 4.

As shown in FIGS. 1 to 3, the insert 1 of the present embodiment is anindexable type insert used by being fixed to a holder. The insert 1generally includes an upper surface 2, a lower surface 3, a side surface4 connected to each of the upper surface 2 and the lower surface 3, athrough hole 6 (fitting hole) extending between the upper surface 2 andthe lower surface 3, and an upper cutting edge 5 located at anintersection of the upper surface 2 and the side surface 4. As shown inFIG. 2, the through hole 6 of the present embodiment is located at amiddle part on each of the upper surface 2 and the lower surface 3.

The insert 1 of the present embodiment is also a so-called negative typeinsert and hence further includes a lower cutting edge 5P located at anintersection of the lower surface 3 and the side surface 4 as shown inFIGS. 1 and 2( b). For example, the insert 1 is preferably configured sothat one side of the upper surface 2 is 5 mm to 100 mm and the thicknessof each of the upper and lower surfaces 2 and 3 is 3 mm to 100 mm.

The insert 1 of the present embodiment has a hexagonal shape(substantially hexagonal shape) as shown in FIG. 2 in a top view and ina bottom view. The phrase “top view” denotes a state that the insert 1is viewed from the upper surface 2. The phrase “bottom view” denotes astate that the insert 1 is viewed from the lower surface 3.

The concept of the phrase “hexagonal shape” includes somewhatdeformation in such a range in which a certain function can beexhibited, without being limited to the case of a strict hexagonal shape(regular hexagon). That is, the hexagonal shape of the presentembodiment includes the cases where, for example, individual sides orvertexes thereof have a slightly curved line shape.

Further, the upper surface 2 (upper cutting edge 5) and the lowersurface 3 alternately have three major corners 21 (first to third majorcorners 21 a to 21 c), each having a first interior angle α, and threeminor corners 22 (first to third minor corners 22 a to 22 c), eachhaving a second interior angle β larger than the first interior angle α.Thus, the insert 1 includes the upper cutting edge 5 and the lowercutting edge 5P of identical shape which are extended from the singlemajor corners 21 to the two adjacent minor corners 22 and 22 on bothsides of the single major corner 21. Therefore, a cutting process can beperformed at each of the three major corners 21 by causing abidirectional rotation for a right-handed operation and a left-handedoperation. That is, the insert 1 of the present embodiment is usable asan insert substantially having the six major corners by using each ofthe three major corners 21 for the right-handed operation and theleft-handed operation.

The first interior angle α is preferably a substantially right angle.The phrase “substantially right angle” denotes an approximately rightangle. Specifically, the substantially right angle in the presentembodiment is in the range of 90°±3°. Particularly, the first interiorangle α is preferably larger than 90°. The second interior angle β ispreferably set in the range of 140° to 150°. The lengths of theindividual sides are preferably identical from the viewpoint of ensuringa large length of the cutting edges contributing to cutting while usingall of the individual sides for the cutting process.

In the insert 1 of the present embodiment, the upper cutting edge 5 islocated over the entire circumference of the upper surface 2. Thereby,the three major corners 21 of the insert 1 are usable for the cuttingprocess. Thus, when the cutting process is performed using the uppercutting edge 5, a part of the lower surface 3 functions as a mountsurface (seating surface) for attaching a holder 11 described later.

As described above, the insert 1 of the present embodiment is theso-called negative type insert allowing both the upper surface 2 and thelower surface 3 to be respectively used as the surface that exhibits arake function as shown in FIGS. 1 and 2. Accordingly, when the cuttingprocess is performed using the lower cutting edge 5P, a part of thelower surface 3 is usable as a rake surface, and a part of the uppersurface 2 is usable as the mount surface (seating surface). That is, theupper surface 2 and the lower surface 3 of the insert 1 of the presentembodiment have the same shape, and both the upper and lower surfacesare usable for the cutting process. Unless otherwise stated, thedescription of the upper surface 2 is applicable to the lower surface 3.

Next, the individual components of the insert 1 of the presentembodiment are described in details.

The upper surface 2 includes a rake surface 23 that has a so-called rakefunction for discharging chips and is inclined downward, namely, towardthe lower surface 3, as going inward from the upper cutting edge 5. Theterm “inward” denotes being located inside the insert 1 with respect tothe upper cutting edge 5 and located closer to the through hole 6 (acentral axis S1). The phrase “central axis S1” is the axis that extendsbetween the upper surface 2 and the lower surface 3, and serves as arotation axis when the insert 1 is rotated in a top view.

The lower surface 3 includes a mount part 31 for mounting the holder 11thereon. The mount part 31 has a shape having six top portions (points):three first top portions 311 a to 311 c (first distance points) spaced adistance a away from a central point O (the central axis S1); and threesecond top portions 312 a to 312 c (second distance points) spaced adistance b away from the central point O (the central axis S1). Thethree first top portions 311 a to 311 c and the three second topportions 312 a to 312 c are disposed alternately. The mount part 31further has a concave part 32 including at least the central point O(the central axis S1). The phrase “central point O” denotes theintersection of the central axis S1 and a line obtained by extending themount part 31 toward the central axis S1 in a side view (refer to FIG.4). The phrase “side view” denotes a state that the insert 1 is viewedfrom the side surface 4.

In the present embodiment, the mount part 31 has a hexagonal shapehaving the six top portions in a bottom view. Specifically, as shown inFIG. 2( b), the mount part 31 has the hexagonal shape with the six topportions of the three first top portions 311 a to 311 c spaced a firstdistance (the distance a) away from the central point O (central axisS1), and the three second top portions 312 a to 312 c spaced a seconddistance (the distance b) away from the central point O (central axisS1). Thus, the individual top portions are respectively intersections ofone side and another side of an outer edge 31 a of the mount part 31,and the intersection of two sides may include a region chamfered in acurved surface and a flat surface as in the case of the presentembodiment.

The first interior angle α at the foregoing major corners 21 is largerthan an interior angle γ at the first top portions 311 constituting theshape of the mount part 31. A second interior angle β at the minorcorners 22 is larger than an interior angle δ at the second top portions312 constituting the shape of the mount part 31. Specifically, there arerelationships of α<γ and β>δ as shown in FIG. 2.

Further, a bisector L1 of the interior angle γ at the first top portion311 and a bisector L2 of the major corners 21 are identical to eachother, and a bisector L3 of the interior angle δ at the second topportion 312 and a bisector L4 of the minor corners 22 are identical toeach other in the bottom view. That is, L1=L2 and L3=L4 as shown in FIG.2( b). These configurations ensure that the insert 1 in the vicinity ofthe major corners 21 has a large thickness and the mount part 31 extendscloser to the lower cutting edge 5P in the vicinity of the major corners22, thereby further downsizing the insert 1.

The mount part 31 has the concave part 32 in the vicinity of the centralpoint O (hereinafter referred to as a “middle part”), and hence themount part 31 is more difficult to contact with a later-describedcontact surface 13 of the holder 11 than the case where the mount part31 is formed by a flat surface and the contact surface 13 of the holder11 is also a flat surface. Additionally, the first top portions 311 andthe second top portions 312 function as a fixing point on the outer edge31 a of the mount part 31, thereby improving the attachment stability ofthe insert 1.

The concave part 32 depends on neither its size nor on its depth. In thepresent embodiment, the mount part 31 has a concave shape. That is, themount part 31 of the present embodiment in its entirety corresponds tothe concave part 32. Specifically, as shown in FIG. 2( b), the outeredge 31 a of the mount part 31 corresponds to an outer edge 32 a of theconcave part 32. According to this configuration, a part of the mountpart 31 located in the vicinity of the outer edge 31 a and the contactsurface 13 of the holder are contacted with each other. This achieves asmaller contact area and an enhanced fixing force, thus improving theattachment stability of the insert 1.

The second top portions 312 have a lower height position than the firsttop portions 311 in a height direction from the upper surface 2 to thelower surface 3. That is, the second top portions 312 are located on anearer side from the upper surface 2 than the first top portions 311. Inother words, the second top portions 312 are located closer to the uppersurface 2, namely, more above than first top portions 311. Morespecifically, as shown in FIG. 3( b), h1>h2 where h1 is a height of thefirst top portions 311 and h2 is a height of the second top portions312. In the present embodiment, these h1 and h2 are measured on thebasis of a vertical plane S1B that is perpendicular to the central axisS1 and passes through a middle point M in a side view. However, themeasurement may be made on the basis of a vertical plane S1 bperpendicular to the central axis S1. According to the foregoingconfiguration, the vicinity of the first top portions 311 having ahigher height position is first brought into contact with the contactsurface 13 of the holder, and the vicinity of the second top portions312 having the lower height position is thereafter brought into contactwith the contact surface 13 of the holder 11. Therefore, the insert 1can be supported by using the vicinity of the first top portions 311 asa major fixing point and the vicinity of the second top portions 312lower than the first top portions 311 as a minor fixing point. Thisconfiguration improves the attachment stability of the insert 1.

The distance a from the central point O (central axis S1) to each of thefirst top portions 311 and the distance b from the central point O(central axis S1) to each of the second top portions 312 may be equal toeach other (a=b), or may be different from each other (a≠b) in a bottomview. In the present embodiment, it is a>b as shown in FIG. 2( b).According to this configuration, the major fixing point (the vicinity ofthe first top portion 311) is located further away from the centralpoint O than the minor fixing point (the vicinity of the second topportion 312), thus making it possible to suppress rotation of the insert1.

Angles formed by the central axis S1 and a straight line connecting thecentral point O and each of the six top portions may be set suitably.For example, all of these angles are different from one another.Alternatively, the angles at the three first top portions 311 may beidentical to each other, and the angles at the three second top portions312 may be identical to each other. In the present embodiment, as shownin FIG. 4, an angle θA formed by the central axis S1 and a straight lineconnecting the central point O and the first top portion 311 isidentical to an angle θB formed by the central axis S1 and a straightline connecting the central point O and the second top portion 312. Thatis, in the mount part 31, the angle θA formed by the central axis S1 anda first extension line L5 obtained by extending the first top portion311 toward the central axis S1, and the angle θB formed by the centralaxis S1 and a second extension line L6 obtained by extending the secondtop portion 312 toward the central axis S1 in a side view are identicalto each other. That is, θA=θB as shown in FIG. 4. This configurationensures effective dispersion of the stress exerted on the middle part ofthe insert 1.

Each of the angles θA and θB is preferably set at 80° to 90°. Forexample, when the mount part 31 is formed in a curved line shape, thefirst extension line L5 may be obtained by extending the first topportion 311 toward the central axis S1 so as to pass through an endportion of the curved surface shaped mount part 31 which is locatedinward. This is also true for the second extension line L6.

The outer edge 31 a of the mount part 31 preferably has a curved surfaceshape protruding toward the upper surface 2 at an intermediate portionof the outer edge 31 a located between the first top portion 311 and thesecond top portion 312. The outer edge 31 a of the mount part 31 of thepresent embodiment has such an arc-like shape that is located closer tothe upper surface 2 at the intermediate portion located between thefirst top portion 312 and the second top portion 312. According to thisconfiguration, the portion of the outer edge 31 a of the mount part 31located between the first top portion 311 and the second top portion 312is difficult to contact with the contact surface 13 of the holder, andhence the vicinity of the first top portion 311 and the vicinity of thesecond top portion 312 can be more surely used as the fixing point.Consequently, the attachment stability of the insert 1 is furtherimproved. Specifically, as shown in FIG. 2( b), a region Q1 is thefixing point in the vicinity of the first top portion 311, and a regionQ2 is the fixing point in the vicinity of the second top portion 312.The regions Q1 and Q2 are respectively brought into contact with thecontact surface 13 of the holder 11.

An outer periphery of the mount part 31 connecting the first top portion311 and the second top portion 312 in a bottom view may be a curved lineor straight line, without being limited thereto. In the presentembodiment, as shown in FIG. 2( b), the outer periphery connecting thefirst top portion 311 and the second top portion 312 adjacent thereto isthe straight line in the bottom view. That is, in the presentembodiment, a portion 31 b of the outer edge 31 a of the mount part 31which connects the first top portion 311 and the second top portion 312adjacent thereto has a straight line shape in the bottom view. Thisconfiguration makes constant a distance to the mount part 31 in thecutting edge 5, and hence the strength of the cutting edge 5 can be madeuniform from one end portion thereof to the other end portion thereof.Therefore, the cutting resistance exerted on the mount part 31 can bemade constant along the outer edge 31 a, thereby further improving theattachment stability of the insert 1.

An inner wall 32 b of the concave part 32 is formed by a circular coneshaped surface with the central point O as a vertex. That is, the innerwall 32 b of the concave part 32 has the circular cone shape having thevertex on the central axis S1. According to this configuration, theinner wall 32 b of the concave part 32 has no corner and hencecontributes to stress mitigation, thereby reducing fracture of theinsert 1.

The concave part 32 has a flat surface 33 that is located around thecentral axis S1 and is perpendicular to the central axis S1. A distanced1 from the first top portion 311 to the flat surface 33 is larger thana distance d2 from the second top portion 312 to the flat surface 33 ina bottom view. That is, d1>d2 as shown in FIG. 2( b). Even if a contactregion extends to the concave part 32 when the insert 1 is adhered tothe contact surface 13 of the holder 11 by a later-described fittingscrew 12 as a fixing member, the above configuration can reduce contactbetween the vicinity of the central axis S1 and the contact surface 13of the holder 11, thus ensuring more stable attachment of the insert 1.

The intersection (lower cutting edge 5P) of the lower surface 3 and theside surface 4 is preferably located at the same position as the secondtop portion 312 or located closer to the upper surface 2, namely, moreabove than the second top portion 312 in a side view. In the presentembodiment, as shown in FIG. 4, a height position of the intersection(lower cutting edge 5P) of the lower surface 2 and the side surface 3 isidentical to or lower than the height position of the second top portion312 of the mount part 31. This configuration reduces a risk that theintersection of the lower surface 2 and the side surface 3, namely, thelower cutting edge 5P is damaged by being strongly pressed against thecontact surface 13 of the holder 11 in the case of the double-sidedinsert 1 as in the present embodiment.

In the present embodiment, the flat surface 33 has a triangular shapehaving a vertex on a bisector of the angle at each of the minor corners22 as shown in FIG. 2( b). According to this configuration, the regionsQ2 have a small area, and hence the force received by the fitting screw12 can effectively be converted to fixing force.

Further in the present embodiment, as shown in FIG. 2( b), the outerperiphery of the through hole 6 is located inside a region surrounded bystraight lines connecting three top portions of the triangular-shapedflat surface 33 in a bottom view. This configuration reduces a risk thatthe fitting screw 12 inserted into the through hole 6 is located higherthan the height of the mount part 31, and generated chips collide withthe fitting screw 12 and scatter in all directions in the case of thedouble-sided insert 1 as in the present embodiment.

The upper cutting edge 5 includes a corner cutting edge 51, a minorcutting edge 52 and a major cutting edge 53. Specifically, as shown inFIGS. 2( a) and 3(a), the upper cutting edge 5 includes the cornercutting edge 51, the minor cutting edge 52 inclined downward, namelytoward the lower surface 3 as separating from the corner cutting edge 51at a first inclination angle θ1 on the basis of a vertical plane S1 bperpendicular to the central axis S1, and the major cutting edge 53inclined downward, namely toward the lower surface 3 as separating fromthe minor cutting edge 52 at a second inclination angle θ2 larger thanthe first inclination angle θ1 on the basis of the vertical plane S1 b.The corner cutting edge 51, the minor cutting edge 52 and the majorcutting edge 53 are located sequentially, for example, from the firstmajor corner 21 a of the three major corners 21 to each of the firstminor corner 22 a and the second minor corner 22 b of the three minorcorners 22, both of which are adjacent to the first major corner 21 a.Therefore, the insert 1 of the present embodiment is capable of havingboth low cutting resistance and excellent fracture resistance incooperation with the major corners 21 having the first interior angle αand the minor corners 22 having the second interior angle β as describedabove.

In the present embodiment, the phrase “first inclination angle θ1”denotes an angle formed by the vertical plane S1 b and a virtualextension line L7 of the minor cutting edge 52, and the phrase “secondinclination angle θ2” denotes an angle formed by the vertical plane S1 band a virtual extension line L8 of the major cutting edge 53. The phrase“virtual extension line L7” denotes a straight line obtained byextending a tangential line at a start point of the minor cutting edge52, namely, an end portion of the minor cutting edge 52 located closerto the corner cutting edge 51. Similarly, the phrase “virtual extensionline L8” denotes a straight line obtained by extending a tangential lineat a start point of the major cutting edge 53, namely, an end portion ofthe major cutting edge 53 located closer to the minor cutting edge 52.

The corner cutting edge 51 is located at an intersection of alater-described major corner side surface 41 of the side surface 4 andthe upper surface 2. The corner cutting edge 51 functions to reducefracture of the major cutting edge 5 due to a cutting force appliedthereto during the cutting process. The corner cutting edge 51 has acurved line shape in a top view. In the present embodiment, the cornercutting edge 51 is perpendicular to the central axis S1 and is parallelto the vertical plane S1 b.

The minor cutting edge 52 is located closer to the corner cutting edge51 in an intersection of a later-described first side surface 42 of theside surface 4 and the upper surface 2. As shown in FIG. 2( a), theminor cutting edge 52 functions as first and second major cutting edgesections 5 a and 5 c together with the major cutting edge 53. The minorcutting edge 52 is also a cutting edge, so-called flat drag, functioningmainly to improve the accuracy of a later-described finished surface 102of a workpiece 100. In the present embodiment, the minor cutting edge 52has a straight line shape.

The major cutting edge 53 is located closer to the first minor corner 22a (second minor corner 22 b) in an intersection of the first sidesurface 42 and the upper surface 2. The major cutting edge 53 functionsmainly to generate chips during the cutting process. In the presentembodiment, the major cutting edge 53 has a concave shape recessedtoward the lower surface 3 in a side view.

Thus, the upper cutting edge 5 is inclined toward the lower surface 3 asgoing to the corner cutting edge 51, the minor cutting edge 52 and themajor cutting edge 53. Consequently, the upper cutting edge 5 has highcutting edge strength on one side thereof closer to the corner cuttingedge 51, and also achieves the low cutting resistance on the other sidethereof closer to the major cutting edge 53. Although the thickness ofthe insert 1 is decreased as going to the corner cutting edge 51, theminor cutting edge 52 and the major cutting edge 53, the distance fromthe through hole 6 to each of the cutting edges is increased. Thisconfiguration ensures high cutting edge strength in each of cutting edgeregions.

Similarly to the upper cutting edge 5, the lower cutting edge 5P alsohas a corner cutting edge 51P, a minor cutting edge 52P and a majorcutting edge 53P. The configurations of the corner cutting edge 51P, theminor cutting edge 52P and the major cutting edge 53P are respectivelyidentical to those of the corner cutting edge 51, the minor cutting edge52 and the major cutting edge 53.

The side surface 4 is the surface functioning as a so-called clearancepart for reducing contact with the workpiece 100. In the presentembodiment, the side surface 4 is perpendicular to the upper surface 2and the lower surface 3 as shown in FIG. 3. Compared with an insertwhose side surface has a clearance angle between the upper surface 2 orthe lower surface 3, the thickness of the insert 1 can be ensured, andhence the insert 1 has excellent fracture resistance.

As a specific configuration, the side surface 4 connected to thehexagonal shaped upper surface 2 has a major corner side surface 41, afirst side surface 42, a minor corner side surface 43 and a second sidesurface 44, which are located sequentially from the first major corner21 a to the second major corner 21 b (third major corner 21 c) as shownin FIG. 3( a). Both the first side surface 42 and the second sidesurface 44 are flat surfaces, and both the major corner side surface 41and the minor corner side surface 43 are curved surfaces.

The through hole 6 functions to fix the insert 1 to the later-describedholder 11. That is, a fitting screw 12 (fixing member) is inserted intothe through hole 6 and is further screwed to the holder 11. A cuttingtool 10 is obtained by fixing the insert 1 to the holder 11 in thismanner. The central axis of the through hole 6 exists at the sameposition as the central axis S1.

<Cutting Tool>

A cutting tool according to an embodiment of the present invention isdescribed in details below with reference to FIGS. 5 to 8.

As shown in FIG. 5, the cutting tool 10 of the present embodimentincludes a plurality of inserts 1 as described above, and a cylindricalshaped holder 11 having a rotation axis S2. The holder 11 is configuredto attach the plurality of inserts 1 thereto by using a fixing member.

The holder 11 has a plurality of insert pockets 11 a at outer peripheralfront ends thereof as shown in FIG. 7. The inserts 1 are respectivelyattached to outer peripheral positions in the insert pockets 11 a.Specifically, when the cutting tool 10 is rotated in the directionindicated by arrow X in FIG. 5, the inserts 1 are attached so that theupper surface (rake surface) 2 is oriented forward in the directionindicated by the arrow X as the rotation direction, and the majorcutting edge 53 is located at the outermost periphery of the holder 11.As an attachment method, the plurality of inserts 1 are respectivelyfixed to the holder 11 by inserting the fitting screw 12 (fixing member)into each of the through holes 6 of the plurality of inserts 1, and byscrewing the fitting screw 12 to the holder 11.

Each of the insert pockets 11 a of the holder 11 has a contact surface13 brought into contact with the insert 1 as shown in FIG. 7.Specifically, when the cutting tool 10 is rotated in the directionindicated by the arrow X, the contact surface 13 is located in adirection opposed to the forward side in the direction indicated by thearrow X as the rotation direction. The contact surface 13 is preferablyformed by a flat surface in order to sufficiently produce the effect ofthe mount parts 31 of the inserts 1.

From the viewpoint of improving the attachment stability of the inserts1, the contact surface 13 preferably has a substantially identical orsimilar shape to the shape of the mount parts 31 of the inserts 1 in abottom view, as shown in FIG. 7( b). The contact surface 13 of thepresent embodiment has a substantially identical shape to the shape ofthe mount parts 31 of the inserts 1 in the bottom view.

Also from the viewpoint of improving the attachment stability of theinserts 1, each of the inserts 1 is preferably contactedly fixed to thethree first top portions 311 of the contact surface 13 of the insertpocket 11 a. For example, in the present embodiment, at least threeregions Q1 including the three first top portions 311 of the insert 1are contactedly fixed to the three first contact regions R1 of the flatcontact surface 13 as shown in FIGS. 2( b) and 7(b). Further in thepresent embodiment, the contact surface 13 of the insert pocket 11 ahas, besides first contact regions R1, three second contact regions R2brought into contact with the three regions Q2 including the threesecond top portions 312 of the insert 1. This configuration furtherimproves the attachment stability of the inserts 1. FIG. 8 shows a statethat the regions Q1 of the insert 1 and the first contact regions R1 ofthe contact surface 13 are contacted with each other, and the regions Q2of the insert 1 and the second contact regions R2 of the contact surface13 are contacted with each other.

The present embodiment has described the aspect that the contact surface13 has the shape substantially identical to the shape of the mount part31 of the insert 1 in the bottom view, without being limited thereto.That is, the contact surface 13 may be configured by reducing orenlarging the shape of the mount part 31 of the insert 1 in the bottomview within a range of possible contact with the regions Q1 and Q2 ofthe insert 1. Alternatively, the contact surface 13 preferably has sucha shape to permit proper contact with the regions Q1 and Q2.

In the present embodiment, as shown in FIG. 6( a), each of the inserts 1is attached to the holder 11 in a state that a first major cuttingsection 5 a of an upper cutting edge 5 extending from a first majorcorner 21 a to a first minor corner 22 a adjacent thereto has a positiveaxial rake angle θa, and a non-cutting section 5 b of the upper cuttingedge 5 extending from the first minor corner 22 a to a second majorcorner 21 b adjacent thereto has a negative axial rake angle θb on thebasis of a parallel plane S2 a parallel to a rotation axis S2 of theholder 11.

The first major cutting section 5 a includes a minor cutting edge 52 anda major cutting edge 53, and has a positive axial rake angle θa both inthe minor cutting edge 52 and the major cutting edge 53 in the presentembodiment. For example, the axial rake angle of the minor cutting edge52 is preferably set at 0° to 10°, and the axial rake angle of the majorcutting edge 53 is preferably set at 5° to 20°. With respect to a curvedline shaped cutting edge, such as the major cutting edge 53, the axialrake angle θa may be measured using a straight line L9 obtained byextending a tangential line at a start point of the major cutting edge53, namely, an end portion thereof located closer to the minor cuttingedge 52. The axial rake angle θb may be measured using a straight lineL10 obtained by extending a tangential line at a start point of thenon-cutting section 5 b, namely, an end portion thereof located closerto the first minor corner 22 a.

As shown in FIG. 6( a), each of the inserts 1 is also attached to theholder 11 in a state that a straight line L11 connecting the first majorcorner 21 a and the second major corner 21 b of the upper cutting edge 5has a negative axial rake angle θc. In other words, the entiretyincluding the first major cutting section 5 a and the non-cuttingsection 5 b has a negative axial rake angle.

The cutting tool 10 is obtained by attaching the inserts 1 to the holder11 in the above manner. A workpiece 100 can be subjected to a facemilling process or a plunge milling process as described later byrotating the cutting tool 10 in the direction indicated by the arrow X.

For example, when the face milling process is performed as shown in FIG.6( b), a cutting target surface 101 is formed by cutting the workpiece100 with the first major cutting section 5 a of the insert 1, and afinished surface 102 is formed by cutting the workpiece 100 with theminor cutting edge 52. Hereat, a setting is made so that the minorcutting edge 52 has a substantially parallel relationship with avertical plane S2 b perpendicular to the rotation axis S2 of the holder11.

<Method of Manufacturing Machined Product>

Next, methods of manufacturing a machined product according to a firstor second embodiment of the present invention are described in detailsbelow with reference to FIGS. 9 and 10.

The method of manufacturing a machined product according to the first orsecond embodiment includes rotating the foregoing cutting tool 10 on thebasis of the rotation axis S2 of the holder 11; bringing the uppercutting edge 5 of the cutting tool 10 being rotated into contact with asurface of the workpiece 100; and separating the cutting tool 10 fromthe workpiece 100. The first and second embodiments are respectivelydescribed in details below.

First Embodiment

The method of manufacturing a machined product according to the firstembodiment is described in details with reference to FIG. 9 by takingthe example of so-called face milling process.

The method of manufacturing a machined product according to the presentembodiment includes the following steps (i) to (iii). In the following,the order of these steps may be changed suitably unless otherwisestated.

The step (i) includes: rotating the cutting tool 10 around the rotationaxis S2 of the holder 11 (cutting tool 10) in the direction indicated bythe arrow X as shown in FIG. 9( a); and bringing the cutting tool 10near the workpiece 100 by moving the cutting tool 10 in the directionindicated by arrow Y1.

The step (ii) is to bring the upper cutting edge 5 of the cutting tool10 being rotated into contact with the surface of the workpiece 100 asshown in FIG. 9( b). In the present embodiment, the step (ii) includesthe following three substeps.

The first substep is to allow the cutting tool 10 being rotated to movein the direction indicated by arrow Z that is the directionperpendicular to the rotation axis S2. Thereby, the workpiece 100 can besubjected to the face milling process.

The second substep is to bring the first major cutting section 5 a ofthe upper cutting edge 5 extending from the first major corner 21 a tothe first minor corner 22 a adjacent thereto in the cutting tool 10being rotated, into contact with the surface of the workpiece 100.Consequently, a cutting target surface of the workpiece 100 cut by beingbrought into contact with the first major cutting section 5 a becomes afinished surface 101 as shown in FIG. 9( b).

The third substep is to bring the minor cutting edge 52 of the uppercutting edge 5 located between the first major corner 21 a and thesecond minor corner 22 b in the cutting tool 10 being rotated, intocontact with the cutting target surface of the workpiece 100 formed bybeing brought into contact with the first major cutting section 5 a.Thereby, a portion of the cutting target surface of the workpiece 100cut by the first major cutting section 5 a in the foregoing secondsubstep, which remains without being directly cut by the first majorcutting section 5 a, can be smoothed by the minor cutting edge 52,resulting in a finished surface 102 as shown in FIG. 9( b).

The step (iii) is to separate the cutting tool 10 from the workpiece 100by moving the cutting tool 10 just as it is in the direction indicatedby arrow Z, as shown in FIG. 9( c).

A machined product 110, which is obtained by cutting the workpiece 100into the desired shape as shown in FIG. 9( c), is manufactured by beingsubjected to the foregoing individual steps.

When the cutting process is continuously performed, for example, it isrequired to repeat the step of bringing the upper cutting edge 5 of thecutting tool 10 into contact with different portions of the workpiece100, while keeping the rotation of the cutting tool 10. When the majorcorner 21 of the upper cutting edge 5 used for the cutting process isworn, the major corner 21 of the upper cutting edge 5 not yet being usedcan be used by rotating the insert 1 by 120° with respect to the centralaxis S1. Additionally in the present embodiment, the single major corner21 of the insert 1 is usable for a reverse-handed cutting process byrotating the cutting tool 10 in the opposite direction to the directionindicated by the arrow X. This permits use as the insert substantiallyhaving the six major corners by using each of the three major corners 21for right-handed and left-handed operations. By changing the rotationdirection of the cutting tool 10 to the opposite direction to thatindicated by the arrow X, the minor cutting edge 52 in the first majorcutting section 5 a functions as a cutting edge for forming the finishedsurface 102. In the present embodiment, the description of the uppercutting edge 5 is also true for the lower cutting edge 5P.

The following modifications are applicable to the foregoing steps. Forexample, in the step (i), the workpiece 100 may be rotated while keepingthe cutting tool 10 stationary. Alternatively, the cutting tool 10 andthe workpiece 100 need to be closer to each other. For example, theworkpiece 100 may be brought near the cutting tool 10. Similarly, in thestep (iii), the workpiece 100 and the cutting tool 10 need to beseparated from each other. For example, the workpiece 100 may beseparated from the cutting tool 10 being held at a predeterminedposition. These modifications are also applicable to the followingsecond embodiment.

Second Embodiment

The method of manufacturing a machined product according to the secondembodiment is described in details with reference to FIG. 10 by takingthe example of so-called plunge milling process.

The method of manufacturing a machined product according to the presentembodiment includes the following steps (i) to (iii). In the following,the order of these steps may be changed suitably unless otherwisestated.

The step (i) includes: rotating the cutting tool 10 around the rotationaxis S2 of the holder 11 (cutting tool 10) in the direction indicated byarrow X as shown in FIG. 10( a); and bringing the cutting tool 10 nearthe workpiece 100 by moving the cutting tool 10 in the directionindicated by arrow Y1.

The step (ii) is to bring the upper cutting edge 5 of the cutting tool10 being rotated into contact with a surface of the workpiece 100 asshown in FIG. 10( b). In the present embodiment, the step (ii) includesthe following three substeps.

The first substep is to allow the cutting tool 10 being rotated to movein the direction indicated by the arrow Y1 that is the directionparallel to the rotation axis S2. Thereby, the workpiece 100 can besubjected to the plunge milling process.

The second substep is to bring the second major cutting section 5 c ofthe upper cutting edge 5 extending from the first major corner 21 a tothe second minor corner 22 b adjacent thereto in the cutting tool 10being rotated, into contact with the surface of the workpiece 100.Consequently, a cutting target surface of the workpiece 100 cut by beingbrought into contact with the second major cutting section 5 c becomes afinished surface 101 as shown in FIG. 10( b).

The third substep is to bring the minor cutting edge 52 of the uppercutting edge 5 located between the first major corner 21 a and the firstminor corner 22 a in the cutting tool 10 being rotated, into contactwith the cutting target surface of the workpiece 100 formed by beingbrought into contact with the second major cutting section 5 c. Thereby,a portion of the cutting target surface of the workpiece 100 cut by thesecond major cutting section 5 c in the foregoing second substep, whichremains without being directly cut by the second major cutting section 5c, can be smoothed by the minor cutting edge 52, resulting in a finishedsurface 102 as shown in FIG. 10( b).

The step (iii) is to separate the cutting tool 10 from the workpiece 100by moving the cutting tool 10 in the direction indicated by arrow Y2, asshown in FIG. 10( c).

A machined product 110, which is obtained by cutting the workpiece 100into the desired shape as shown in FIG. 10( c), is manufactured by beingsubjected to the foregoing individual steps.

When the cutting process is continuously performed, it is required toperform similarly to the foregoing first embodiment.

While the several embodiments of the present invention have beenillustrated and described, it is to be understood that the presentinvention is not limited to the foregoing embodiments but variouschanges and modifications can be made therein without departing from thespirit or scope of the present invention.

For example, the upper surface 2 and the lower surface 3 may havedifferent colors though not particularly mentioned in the inserts 1 ofthe foregoing embodiments. Specifically, for example, when an insertbody is made of silver-colored cemented carbide, either the uppersurface 2 or the lower surface 3 is preferably coated with gold-coloredtitanium nitride (TiN). In the negative-type insert, both the uppersurface 2 and the lower surface 3 function as the rake surface, andhence an erroneous attachment of the inserts might occur. By coatingeither the upper surface 2 or the lower surface 3 with TiN, a surfacecoated with TiN and an uncoated surface have different colors. It istherefore capable of clearly distinguishing between these two surfaces,thereby reducing misrecognition when attaching the inserts 1. Hereat, acoating target surface of either the upper surface 2 or the lowersurface 3 need not be entirely coated. A similar effect is obtainable bycoating, for example, a part of the coating target surface (e.g., aportion other than the cutting edges) with TiN. The material used forthe coating is not limited to TiN as long as one can recognize a colordifference between the upper surface 2 and the lower surface 3. Forexample, when the insert body is made of cemented carbide, it is alsopossible to employ bright reddish brown colored titanium carbonitride(TiCN), dark reddish brown colored titanium aluminum nitride (TiAlN), orthe like.

Although not being particularly described in the inserts 1 of theforegoing embodiments, the upper cutting edge 5 may be configured tohave a land (not shown) substantially parallel to the vertical plane S1b. This configuration improves the strength of the upper cutting edge 5,thus making it possible to suitably use the inserts 1 under machiningconditions of so-called heavy-duty cutting.

Although the upper surface 2 of the inserts 1 of the foregoingembodiments has the hexagonal shape, the upper surface 2 may have anypolygonal shape other than the hexagonal shape.

1. A cutting insert, comprising: an upper surface; a lower surface; aside surface connected to each of the upper surface and the lowersurface; and an upper cutting edge located at an intersection of theupper surface and the side surface, wherein the lower surface comprisesa mount part comprising alternately three first top portions spaced adistance a away from a central axis extending between the upper andlower surfaces and three second top portions spaced a distance b awayfrom the central axis in a bottom view, the mount part furthercomprising a concave part including at least the central axis, and thesecond top portions are located closer to the upper surface than thefirst top portions.
 2. The cutting insert according to claim 1, whereinthe mount part in its entirety corresponds to the concave part.
 3. Thecutting insert according to claim 1, wherein the distance a and thedistance b have a relationship of a>b in a bottom view.
 4. The cuttinginsert according to any one of claim 1, wherein in the mount part, anangle formed by the central axis and a first extension line obtained byextending the first top portion toward the central axis is equal to anangle formed by the central axis and a second extension line obtained byextending the second top portion toward the central axis in a side view.5. The cutting insert according to any one of claim 1, wherein an outeredge of the mount part has a curved line shape protruded toward theupper surface at an intermediate portion of the outer edge locatedbetween the first top portion and the second top portion.
 6. The cuttinginsert according to any one of claim 1, wherein a portion of the outeredge of the mount part connecting the first top portion and the secondtop portion adjacent to the first top portion has a straight line shapein a bottom view.
 7. The cutting insert according to any one of claim 1,wherein an inner wall of the concave part has a circular cone shapehaving a vertex on the central axis.
 8. The cutting insert according toany one of claim 1, wherein the concave part comprises a flat surfacelocated closer to the central axis and perpendicular to the centralaxis, and a distance from the first top portion to the flat surface islarger than a distance from the second top portion to the flat surfacein a bottom view.
 9. The cutting insert according to any one of claim 1,wherein the upper cutting edge further comprises a major corner having afirst interior angle smaller than an interior angle at the first topportion, and a minor corner having a second interior angle larger thanan interior angle at the second top portion, wherein a bisector of theinterior angle at the first top portion and a bisector of the majorcorner are identical to each other, and a bisector of the interior angleat the second top portion and a bisector of the minor corner areidentical to each other in a bottom view.
 10. The cutting insertaccording to any one of claim 1, wherein an intersection of the lowersurface and the side surface is located at a position identical to thatof the second top portion or located closer to the upper surface thanthe second top portion in a side view.
 11. The cutting insert accordingto any one of claim 8, further comprising: a through hole extendingbetween the upper surface and the lower surface, wherein outer peripheryof the through hole is located inside the flat surface in a bottom view.12. A cutting tool, comprising: a cutting insert according to any one ofclaim 1; and a holder configured to attach the cutting insert thereto.13. The cutting tool according to claim 12, wherein the holder comprisesan insert pocket at an outer peripheral front end thereof, the insertpocket being configured to attach the cutting insert thereto, the insertpocket comprises a contact surface brought into contact with the mountpart of the cutting insert, and the cutting insert is attached to theholder so as to bring the first top portion into contact with thecontact surface.
 14. A method of manufacturing a machined product,comprising: rotating a cutting tool according to claim 12 on a basis ofa rotation axis of the holder; bringing the upper cutting edge of thecutting tool being rotated into contact with a surface of a workpiece;and separating the cutting tool from the workpiece.